1. Field of the Invention
The invention is concerned with a hard facing tungsten alloy useful as a facing or coating for a wide variety of substrate materials, including iron and steel based materials. The alloy is particularly useful as a facing for piston rings, including compression and oil control rings for internal combustion engine pistons.
2. Description of the Prior Art
Piston rings, including compression rings and oil control rings are normally coated with a hard facing metal. A typical example is a flame spray applied molybdenum hard facing material which affords excellent performance for piston rings in high-compression, high temperature operating internal combustion engines. Another coating or facing for piston rings is one composed of a refractory metal carbide such as tungsten carbide. In the situation where tungsten forms the bulk of the alloy coating, to date it has been thought that the tungsten must be in the form of a compound such as tungsten carbide. Efforts to make a piston facing containing tungsten itself as a separate phase have been unsuccessful, since the tungsten has been found to be too soft, and does not protect the piston ring under typical operating conditions to the sought-after degree of performance.
It would therefore be a substantial advance in the art if an alloy were discovered which contained a substantial amount of tungsten per se as a separate phase and yet was sufficiently hard to be used as a coating for piston rings in high-compression internal combustion engines.